Many networks such as local and wide area networks (LAN/WAN) structures are used to carry and distribute data communication signals between devices. Various network elements include hubs, switches, routers, and bridges, peripheral devices, such as, but not limited to, printers, data servers, desktop personal computers (PCs), portable PCs and personal data assistants (PDAs) equipped with network interface cards. Devices that connect to the network structure use power to enable operation. Power of the devices may be supplied by either an internal or an external power supply such as batteries or an AC power via a connection to an electrical outlet.
Some network solutions can distribute power over the network in combination with data communications. Power distribution over a network consolidates power and data communications over a single network connection to reduce installation costs, ensures power to network elements in the event of a traditional power failure, and enables reduction in the number of power cables, AC to DC adapters, and/or AC power supplies which may create fire and physical hazards. Additionally, power distributed over a network such as an Ethernet network may function as an uninterruptible power supply (UPS) to components or devices that normally would be powered using a dedicated UPS.
Additionally, network appliances, for example voice-over-Internet-Protocol (VoIP) telephones and other devices, are increasingly deployed and consume power. When compared to traditional counterparts, network appliances use an additional power feed. One drawback of VoIP telephony is that in the event of a power failure the ability to contact emergency services via an independently powered telephone is removed. The ability to distribute power to network appliances or circuits enable network appliances such as a VoIP telephone to operate in a fashion similar to ordinary analog telephone networks currently in use.
Distribution of power over Ethernet (PoE) network connections is in part governed by the Institute of Electrical and Electronics Engineers (IEEE) Standard 802.3 and other relevant standards, standards that are incorporated herein by reference. However, power distribution schemes within a network environment typically employ cumbersome, real estate intensive, magnetic transformers. Additionally, power-over-Ethernet (PoE) specifications under the IEEE 802.3 standard are stringent and often limit allowable power.
IEEE 802.3 for PoE systems specifies standards for electromagnetic interference (EMI) immunity and emissions. EMI emissions can be caused by inductive coupling of external common mode sources coupling to the twisted pair cable or power supply wall adaptor. In addition a powered device (PD) can generate electromagnetic emissions through common mode noise and transmit the noise on the twisted pair cable or power supply cable, thus radiating emissions outside an enclosure for the powered device, violating FCC radiation specifications FCC/CISPRR Class B.
IEEE 802.3 for PoE systems specifies standards for immunity to overvoltage and surge events which can be caused by inductive coupling of external lightning events or simply by static electricity buildup on Ethernet cabling. The discharge of overvoltage or surge energy into sub-micron semiconductor devices can easily become destructive. In conventional PoE systems, expensive and ruggedized external components such as sidactors are typically added to shield silicon-based devices from the stresses of external surge events by clamping the surge voltage and forming a large current path for the surge to ground, a surge path that can ruin performance of sensitive circuits unless routed around the circuits. Accordingly, protective components are dependant on board parasitic and layouts which can vary, creating difficulty in ensuring consistent performance. In addition, the components are typically high capacitance and tend to degrade overall system performance in high speed communication links.